Here is my logo for your consideration. I made a clean, memorable circle crest containing a 30 combined with a g. Simple, yet memorable and visually pleasing. Thanks for looking.
I really like the concept. It very much reminds me of stamp. But I think the 0 is lost in the g. Can you return the g to a o and maybe make the black background look more like a G? I don't know if that would look right, but it looks like 3G (or 3g) at the moment.
Thanks for the really fast feedback; much appreciated. I have submitted some new variations for you, with the 30 inside of a g-shaped stamp. (#51, #52, #53, #54)